1. Technical Field
The present invention relates to a calibration method for calibrating an instrument for measuring a biogenic substance, using near-infrared spectral spectroscopy, and in particular, to a non-infesting calibration method for calibrating an instrument for measuring a biogenic substance, using near-infrared spectral spectroscopy, by the use of an instrument for measuring a biogenic substance, using a confocal optical system, as a reference.
2. Related Art
In the case of measuring concentration of a blood component, such as blood glucose, and so forth, in the past, blood has been often actually collected from a human body by use of a syringe, or by piercing a fingertip, or an earlobe. In contrast, there have lately been proposed techniques (refer to Patent Documents 1 to 4, and Non-patent Document 1) whereby a biological object is irradiated with light instead of collecting blood through infestation of the biological object, carried out as in the past, and reflected light from the biological object, and light transmitted through the biological object are detected, thereby measuring concentration of a blood component as a measurement subject, and so forth on the basis of a degree of light absorbed (absorbance) by the biological object.
With the technique described in Non-patent Document 1, in particular, with skin tissues of a human body, comprising epidermal tissues a1, dermal tissues a2, and hypodermal tissues a3, as shown in FIG. 2, capillary vessels are not well developed inside the epidermal tissues a1, and the hypodermal tissues a3 is made up mainly of adipose tissues; in contrast, capillary vessels are well developed inside the tissues of the dermal tissues a2 present between the epidermal tissues a1, and the hypodermal tissues a3, and since glucose having high permeability undergoes permeation into tissues from within a blood vessel, it is presumed that there exists correlation between concentration of glucose in the dermal tissues a2, and a blood glucose value in blood.
Under such presumption, there has been proposed a near-infrared spectroscopic analysis whereby a probe P is butted against a skin, the probe P being made up of an optical fiber Fin for incident light, and an optical fiber Fdet for detection, the skin is irradiated with a near-infrared ray R emitted from the optical fiber Fin for incident light to cause the near-infrared ray R to be transmitted through the dermal tissues a2 before being detected by the optical fiber Fdet for detection, the concentration of glucose in the dermal tissues a2 is measured from absorbance of the near-infrared ray R, and a blood glucose value in blood is predicted on the basis of results of such a measurement.
Further, in Patent Document 1, there is described an instrument for measuring a biogenic substance, using a confocal optical system, as shown in FIG. 3. FIG. 3 is briefly explained about hereinafter.
The instrument 1 for measuring a biogenic substance is comprised of a confocal optical system 2 for collecting data on a biogenic substance of a biological object A, and a data analysis system 3 for analyzing the data obtained.
The confocal optical system 2 is provided with a placement board 21, on which a biological object A, such as, for example, an arm of a test subject, is placed. Provided above the biological object A is a laser 22 capable of emitting laser beams at two or more wavelengths, and in this case, use is made of a wavelength-variable laser.
A collimator lens 23 for turning a laser beam into parallel rays is disposed in the back stage of the laser 22, and a half mirror 24 having a tilt by approximately 45° against the optical axis is disposed in the back stage of the collimator lens 23, the laser beam being transmitted through the half mirror 24.
An objective lens 25 for converging the parallel rays that are turned from the laser beam emitted from the laser 22 is disposed in the back stage of the half mirror 24, the laser beam irradiating internal tissues of the biological object A.
Reflected light that is reflected by the internal tissues of the biological object A is refracted by the objective lens 25 to be turned into parallel rays to be subsequently reflected by the half mirror 24, whereupon an optical path thereof is converted by approximately 90°.
Disposed on a side of the half mirror 24 is a lens 26 for receiving the reflected light whose optical path is converted, and converging the same, and the light reflected by the half mirror 24 is converged at the position of a pinhole 27 provided on a side of the lens 26 to pass through the pinhole 27 before being received by a photodetector 28 made up of, for example, a photodiode.
The pinhole 27 can be configured in such a way as to enable a quantity of the reflected light passing therethrough to be adjusted by adoption of, for example, a configuration wherein the pinhole 27 is provided with a diaphragm, a plurality of pinholes are provided so as to be switched over among them, and so forth.
Current, and voltage, varying in intensity and magnitude, according to a quantity of the reflected light as received, are outputted as data signals, respectively, from the photodetector 28, and the data signals undergo an A/D conversion by the agency of an A/D converter 29 to be transmitted to the data analysis system 3 of the instrument 1 for measuring a biogenic substance.
As shown in FIG. 4, the data analysis system 3 is made up of a computer wherein a CPU 31, a ROM 32, a RAM 33, and an input/output interface 34 are connected to a bus 35. The CPU 31 reads various programs stored in the ROM 32, such as a program for data analysis, and so forth, to be expanded as appropriate on the RAM 33, thereby executing various processing.
In data analysis, the CPU 31 executes quantitative determination of the biogenic substance of the biological object A on the basis of a plurality of the data signals inputted from the photodetector 28 via the A/D converter 29, and the input/output interface 34 due to emission of the respective laser beams varying in wavelength, at two or more wavelengths.
More specifically, in the case of determining a blood glucose value, that is, the concentration of glucose in blood, since an analytical curve indicating a correlation between the concentration of glucose in blood, and absorbance of a laser beam, as shown in FIG. 5, is stored in the ROM 32, the CPU 31 executes the quantitative determination of the biogenic substance of the biological object A on the basis of the analytical curve.